CVE-2026-78050

Executive Summary

CVE-2026-78050 is a critical stack-based buffer overflow vulnerability (CWE-119) in the Comfast CF-N1-S wireless router firmware version 2.6.0.1. The flaw resides in the Web Management component, specifically within the function sub_41AD7C reachable via the /cgi-bin/mbox-config?method=SET&section=ntp_timezone endpoint. Successful exploitation allows an authenticated remote attacker to achieve arbitrary code execution with root privileges on the device, potentially leading to full device compromise, network pivoting, and lateral movement. With a CVSS score of 9.9 and public exploit availability, this vulnerability poses an immediate and severe risk to all deployed CF-N1-S devices running the affected firmware.

Technical Analysis

The vulnerability is a classic stack-based buffer overflow triggered by the manipulation of the timestr and ntp_client_enabled arguments submitted to the NTP timezone configuration endpoint of the web management interface. The affected function, sub_41AD7C, copies attacker-controlled input into a fixed-size stack buffer without performing adequate bounds checking. When the input length exceeds the buffer capacity, adjacent stack memory—including the saved return address and other control data—is overwritten, enabling an attacker to redirect program execution flow.

Key technical attributes derived from the CVE data:

• Affected Endpoint: /cgi-bin/mbox-config?method=SET&section=ntp_timezone
• Affected Function: sub_41AD7C (stack copy routine, likely a strcpy/sprintf derivative)
• Attack Vectors: The timestr parameter (accepts NTP time string data) and ntp_client_enabled parameter (accepts an enable/disable flag, but the parsing routine may overflow when processing malformed numeric content)
• Authentication Requirement: CVSS vector indicates PR:L (Low Privilege Required), meaning the attacker must have valid credentials for the device's web management interface—typically the default admin credentials many users fail to change
• Network Context: AV:N confirms remote exploitability over the network; the web management service typically listens on TCP port 80/443
• Impact Scope: S:C denotes a scope change, meaning the compromise extends beyond the vulnerable component to the broader system context—in a router, this implies full OS-level code execution

The absence of stack canaries (common in embedded firmware of this vintage), non-executable stack protections, and address space layout randomization (ASLR) significantly lowers exploitation complexity. The published public exploit indicates that generic ROP-chain or direct return-address overwrite techniques are effective against this target.

Exploitation Scenarios

The attack chain is as follows:

Note: No public PoC details were provided in the CVE data beyond the vulnerability disclosure. The following steps are inferred from the vulnerability class and the specific endpoint/function details provided.

1. Reconnaissance/Target Identification: An attacker scans for Comfast CF-N1-S devices using network discovery tools (e.g., Shodan, Censys) with queries such as http.title:"CF-N1-S" or by probing common router management ports (80, 443, 8080). The web management interface is identified by its distinctive mbox-config CGI endpoint.

2. Authentication Bypass/Credential Access: The attacker must authenticate to the web management interface. Given the PR:L requirement, common attack vectors include:

   • Using default credentials (e.g., admin/admin) that remain unchanged
   • Brute-forcing weak passwords
   • Leveraging previously compromised credentials from phishing or credential-stuffing campaigns

3. Triggering the Buffer Overflow: The authenticated attacker crafts an HTTP POST request to /cgi-bin/mbox-config?method=SET&section=ntp_timezone with a specifically crafted timestr parameter or a malformed ntp_client_enabled value. The payload contains:

   • A long sequence of characters (typically 500+ bytes) to exceed the stack buffer boundary in sub_41AD7C
   • Crafted data padding the overflow to precisely overwrite the saved return address (or a function pointer) with the address of attacker-controlled shellcode or a ROP gadget chain

4. Code Execution and Post-Exploitation: Upon successful return-address overwrite, execution redirects to attacker-controlled code. On the router platform, the payload is most likely an ARM or MIPS architecture shellcode (depending on the router's CPU, commonly MediaTek or Broadcom chipsets). Post-exploitation activities include:

   • Establishing a reverse shell to the attacker's C2 infrastructure
   • Modifying firewall rules and routing tables to enable network pivoting into the internal LAN
   • Intercepting DNS traffic to redirect users to malicious domains
   • Deploying persistent backdoors (e.g., adding a hidden administrative account)
   • Using the compromised router as a stepping stone for further attacks on the internal network

The scope change (S:C) indicates that the attacker moves from the web application context to the full operating system context, granting the highest privilege level on the embedded device.

Impact Assessment

The CVSS 9.9 severity reflects the trifecta of high impact on confidentiality, integrity, and availability (C:H/I:H/A:H), combined with broad scope change (S:C). Business impact considerations:

• Complete Device Compromise: The router is fully controlled by the attacker, rendering it an untrusted network element
• Network Eavesdropping: All traffic traversing the router can be intercepted, including internal LAN traffic
• Data Exfiltration: Sensitive corporate data crossing the device can be captured and exfiltrated
• Availability Loss: An attacker can brick the device or create persistent denial-of-service conditions
• Lateral Movement Enablement: The compromised router typically sits at the network perimeter, providing the attacker a foothold into the internal network—effectively bypassing perimeter security controls

Affected Systems: All Comfast CF-N1-S devices running firmware version 2.6.0.1. Since no patch is available (Patch Confidence: 0/4), any deployed device with this firmware is at risk.

Blast Radius: The vulnerability's network-based attack vector (AV:N) from the LAN or WAN perspective means any authenticated user of the device—or an external attacker who obtains valid credentials—can exploit it. The public exploit availability lowers the barrier-to-entry, enabling even script-kiddie-level attackers to weaponize this flaw.

Detection Guidance

Detection rules below target the post-authentication anomalous HTTP traffic to the vulnerable endpoint. These rules should be tuned to the organization's environment to reduce false positives.

Sigma Rule

title: Comfast CF-N1-S NTP Timezone Buffer Overflow Attempt
id: 9f8b3d7c-6e42-4a91-93ff-8a3f0e15c72d
status: experimental
description: Detects oversized requests to the mbox-config NTP timezone endpoint indicative of stack buffer overflow exploitation
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2026-78050
author: Valtersit Threat Intelligence
date: 2026/01/01
logsource:
    category: webserver
    product: nginx
    service: http
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: 'mbox-config'
        cs-uri-query|contains: 'section=ntp_timezone'
    filter_short:
        cs-bytes|lt: 2048
    condition: selection and not filter_short
falsepositives:
    - Legitimate large NTP configuration updates (rare, typically under 1KB)
    - Custom scripts updating timezone settings programmatically
level: high
tags:
    - attack.t1190
    - cve.2026-78050
    - cwe.119

YARA Rule

rule CVE2026_78050_Comfast_BufferOverflow_Payload
{
    meta:
        author = "Valtersit Threat Intelligence"
        description = "Detects HTTP payloads targeting the Comfast CF-N1-S NTP timezone buffer overflow"
        date = "2026-01-01"
        cve = "CVE-2026-78050"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-78050"
    strings:
        $endpoint = "mbox-config?method=SET&section=ntp_timezone" ascii wide nocase
        $param_ts = "timestr=" ascii wide nocase
        $param_ne = "ntp_client_enabled=" ascii wide nocase
        $overflow_pattern = /timestr=[A-Za-z0-9%]{500,}/ nocase
    condition:
        ($endpoint and ($param_ts or $param_ne)) and $overflow_pattern
}

Suricata IDS Rule

alert http any any -> $HOME_NET any (msg:"ET EXPLOIT Comfast CF-N1-S mbox-config NTP timezone buffer overflow attempt"; flow:to_server,established; content:"mbox-config"; http_uri; content:"section=ntp_timezone"; http_uri; content:"timestr="; http_uri; isdataat:500,relative; dsize:>1000; reference:cve,2026-78050; reference:url,https://nvd.nist.gov/vuln/detail/CVE-2026-78050; classtype:attempted-admin; sid:2026078050; rev:1;)

Elastic Detection

sequence by host.name with maxspan=1m
  [ network where event.type == "start" and destination.port in (80, 443) and
    network.protocol == "http" ] // Identify HTTP request to web management
  [ http where http.request.method == "POST" and
    url.path contains "mbox-config" and
    url.query contains "section=ntp_timezone" and
    url.query contains "timestr=" and
    (url.query.length > 500 or request.bytes > 1000) ]

Splunk SPL Query

index=web sourcetype=access_combined (uri_path="/cgi-bin/mbox-config" OR uri="/cgi-bin/mbox-config*")
| where method IN ("POST", "GET")
| where like(uri_query, "%section=ntp_timezone%")
| where len(uri_query) > 1000
| eval danger_score = len(uri_query)
| table _time, src_ip, dest_ip, uri, uri_query, status, user
| sort - danger_score
| limit 50

Wazuh OSSEC Rule

<group name="webserver,">
  <rule id="100850" level="12">
    <if_sid>31100</if_sid>
    <url>/cgi-bin/mbox-config</url>
    <description>Comfast CF-N1-S NTP Timezone buffer overflow exploitation attempt (CVE-2026-78050)</description>
    <group>attack.t1190,cve-2026-78050,cwe-119,</group>
    <mitre>
      <id>T1190</id>
    </mitre>
  </rule>
  <rule id="100851" level="14">
    <if_sid>100850</if_sid>
    <regex>timestr=.</regex>
    <regex type="length">500</regex>
    <description>Large timestr parameter detected in mbox-config request - likely buffer overflow payload</description>
    <group>attack.t1190,cve-2026-78050,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch Confidence: 0/4 — UNPATCHED. No vendor patch, firmware update, or workaround has been identified from any tracked source. The vendor (Comfast) has not released an advisory or fix as of the last data update.

Immediate Mitigations (compensating controls):

1. Restrict Network Access: Block external (WAN-side) access to the router's web management interface using access control lists on the uplink firewall. Only allow management from trusted internal management VLANs.
2. Change Default Credentials: Ensure all CF-N1-S devices have strong, unique admin credentials. Disable default accounts if possible. This reduces the likelihood of an attacker meeting the PR:L requirement.
3. Apply YARA/Sigma rules: Deploy the detection signatures above on network intrusion detection systems (IDS/IPS) to alert on exploitation attempts.
4. Monitor Traffic: Enable logging on the device (if supported) and on perimeter firewalls to capture requests to /cgi-bin/mbox-config.
5. Segment the Network: Place deployed routers on isolated VLANs to limit blast radius in case of compromise.

Patch/Upgrade Steps:

• Check the Comfast official website and firmware update page for any newly released firmware for the CF-N1-S model (visit vendor site regularly).
• If a patched firmware becomes available, follow the vendor's upgrade process carefully (typically via upload through the web interface or TFTP recovery).
• Prior to patching, verify firmware integrity using checksums provided by the vendor.

Long-Term Hardening:

• Replace End-of-Life Devices: If Comfast does not provide a patch within a reasonable timeframe (30–60 days), strongly consider replacing the CF-N1-S with a vendor that maintains active security support.
• Disable Remote Management: If remote management is not strictly required, disable it entirely. If required, enforce VPN-based access.
• Network Segmentation: Migrate critical business functions away from consumer-grade routers; deploy enterprise-grade firewalls with proper security features.
• Vulnerability Management: Add this CVE to your vulnerability scanning process to track device exposure across your fleet.
• Incident Response Preparedness: Develop an IR playbook for router compromise events, including device isolation and forensic capture procedures.
• Firmware Baseline: Maintain a hardened firmware baseline for all network equipment.

References

1. NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2026-78050 (Official NVD record with CVSS details)
2. Comfast Official Website: https://www.comfast.com.cn (Vendor site — has not published a security advisory for this CVE at the time of writing)
3. CWE-119 Details: https://cwe.mitre.org/data/definitions/119.html (MITRE CWE definition — Improper Restriction of Operations within the Bounds of a Memory Buffer)
4. ATT&CK Technique T1190: https://attack.mitre.org/techniques/T1190/ (Exploit Public-Facing Application — applicable MITRE ATT&CK framework reference)
5. CISA Known Exploited Vulnerabilities Catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog (CVE-2026-78050 is NOT listed at this time — verified)

Threat Actor Campaigns: No specific threat actor campaigns have been publicly attributed to this CVE as of the report date. The public availability of exploit code raises the risk of opportunistic mass exploitation by botnet operators (e.g., Mirai-variant botnets targeting IoT devices) and commodity threat actors. Monitor threat intelligence feeds for emerging campaigns leveraging this vulnerability.